This invention relates to a hydraulic piston-cylinder unit for work machines and, more particularly, to a cylinder chamber formed below the base of the piston and a cylinder chamber on a side of the piston that carries piston ring that are each connected via a respective line to a manually actuatable control valve which is coupled to an oil storage tank and an oil feed pump wherein a clamping valve is inserted in the line leading to the cylinder chamber formed below the base of the piston.
It is well known for a double action piston-cylinder unit to be used for raising and lowering an arm fitted t o the front of a self-propelled agricultural machine that is equipped with a device for seating a frontal attachment. Due to the use of a double action piston-cylinder unit, it follows that the frontal attachment can be driven upwardly or downwardly for pressing against the ground. It is not possible for the frontal attachment to oscillate of its own accord in the vertical direction. Therefore, during harvesting, an operator of an agricultural harvesting machine may be faced with the problem of making a particular frontal attachment, as a beet harvester, follow every unevenness in the ground whilst simultaneously ensuring that the frontal attachment rests on the earth with as constant a pressure as possible. To accomplish this task, the operator of the machine must exert maximum concentration even though the result will still be imperfect. To make it even more difficult, there is the additional problem that the actual position of the frontal attachment on the ground is very difficult to assess from the operator""s viewpoint.
The present invention is directed to overcoming one or more of the problems as set forth above.
In an aspect of the present invention, a hydraulic piston-cylinder unit is disclosed. The piston-cylinder unit includes a cylinder chamber formed below a base of a piston and a cylinder chamber on a side of the piston carrying piston rings that are each connected via a respective line to a manually actuatable control valve which is coupled to an oil storage tank and an oil feed pump. A clamping valve is inserted in the line leading to the cylinder chamber formed below the base of the piston. The invention comprises a first line connectable between the control valve and the cylinder chamber formed below the base of the piston. A second line is connectable with the oil storage tank and is branched off from the first line connectable between the control valve and the cylinder chamber formed below the base of the piston. A pilot controlled seat valve and an adjustable pressure regulating valve are connected within the second line.
The present invention hydraulic double action piston-cylinder includes a pilot controlled seat valve and a pressure regulating valve that are located in a manner within a line connectable with an oil storage tank and branched off from a line connectable between a control valve and a cylinder chamber formed below a base of a piston to allow for a frontal attachment of a work machine to accurately copy the actual contour of the ground without involving too great a degree of concentration for an operator. At the same time, the present invention provides that the frontal attachment rests on the ground with the same amount of pre-selected force irrespective of the frontal attachment being used.